Single scan irradiation for crystallization of thin films

ABSTRACT

A method of processing a polycrystalline film on a substrate includes generating laser pulses, directing the laser pulses through a mask to generate patterned laser beams, each having a length l′, a width w′, and a spacing between adjacent beams d′; irradiating a region of the film with the patterned beams, said beams having an intensity sufficient to melt and to induce crystallization of the irradiated portion of the film, wherein the film region is irradiated n times; and after irradiation of each film portion, translating the film and/or the mask, in the x- and y-directions. The distance of translation in the y-direction is about l′/n-δ, where δ is a value selected to overlap the beamlets from one irradiation step to the next. The distance of translation in the x-direction is selected such that the film is moved a distance of about λ′ after n irradiations, where λ′=w′+d′.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/944,350, filed Sep. 17, 2004 and entitled “Single Scan Irradiationfor Crystallization of Thin Films,” the entire contents of which areincorporated by reference, which claims priority under 35 U.S.C. §119(e)to co-pending U.S. Application Ser. No. 60/504,270, filed Sep. 19, 2003,and entitled “Single Scan Irradiation for Crystallization of ThinFilms,” the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to methods and systems for processing thin filmmaterial, and more particularly to forming large-grained,grain-boundary-location controlled thin films from amorphous orpolycrystalline thin films using laser irradiation. In particular thepresent invention relates to methods and systems for the production ofintegrated thin film transistors.

BACKGROUND OF THE INVENTION

In recent years, various techniques for crystallizing or improving thecrystallinity of an amorphous or polycrystalline semiconductor film havebeen investigated. This technology is used in the manufacture of avariety of devices, such as image sensors and active-matrixliquid-crystal display (AMLCD) devices. In the latter, a regular arrayof thin-film transistors (TFT) is fabricated on an appropriatetransparent substrate, and each transistor serves as a pixel controller.

Sequential lateral solidification (SLS) using an excimer laser is onemethod for fabricating high quality polycrystalline films having largeand uniform grains. A large-grained polycrystalline film can exhibitenhanced switching characteristics because the number of grainboundaries in the direction of electron flow is reduced. SLS processingcontrols the location of grain boundaries. U.S. Pat. Nos. 6,322,625,6,368,945, 6,555,449 and 6,573,531 issued to Dr. James Im, the entiredisclosures of which are incorporated herein by reference, and which areassigned to the common assignee of the present application, describesuch SLS systems and processes.

In an SLS process, an initially amorphous or poly crystalline film (forinstance, a continuous wave (CW)-processed Si film, an as-depositedfilm, or solid-phase crystallized film) is irradiated by a narrow laserbeamlet. The beamlet is formed by passing a laser beam through apatterned mask, which is projected onto the surface of the film. Thebeamlet melts the precursor film, and the melted film thenrecrystallizes to form one or more crystals. The crystals grow primarilyinward from edges of the irradiated area towards the center. After aninitial beamlet has crystallized a portion of the film, a second beamletirradiates the film at a location less than the lateral growth lengthfrom the previous beamlet. In the newly irradiated film location,crystal grains grow laterally from the crystal seeds of thepolycrystalline material formed in the previous step. As a result ofthis lateral growth, the crystals attain high quality along thedirection of the advancing beamlet. The elongated crystal grains aregenerally perpendicular to the length of the narrow beam and areseparated by grain boundaries that run approximately parallel to thelong grain axes.

Although the resultant polycrystalline films have elongated grains withenhanced mobilities, the many iterative steps of irradiation andtranslation result in low throughput rates. There is a need to increasethe throughput rates in the processing of semiconductor materialswithout sacrificing the quality of the processed materials.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a single scan irradiationtechnique for crystallization of thin films. In other aspects, thepresent invention provides methods and systems for processing amorphousor polycrystalline precursor films to produce films of highercrystallinity. The present invention also provides polycrystalline filmsof varying degrees of crystallinity and crystalline grain orientation.

In one aspect of the present invention, a method is provided forprocessing a selected region of a film in a single laser scan across theselected film region. The method includes translating a film in a firstdirection, e.g., y-direction, while simultaneously translating a mask ina second direction, e.g., the x-direction and/or y-direction. The maskprojects a patterned laser beam or a set of patterned laser beams(hereinafter referred to as a “a patterned laser beam”) onto the filmsurface. The mask pattern and the translation pathways and speeds forthe film and mask are selected so that the selected film region issubstantially completely crystallized in a single scan of the filmregion by the laser.

By “completely crystallized” it is meant that the selected region of thefilm possesses the desired microstructure and crystal orientation, sothat no further laser scanning of the region is required. In someinstances, the entire surface area of the selected regions iscrystallized. In other instances, bands or islands of the selectedregions are crystallized. A film region is considered “completelycrystallized” if the desired level of crystallization is achieved in theselected region of the film.

According to one aspect of the invention, a method of crystallizing afilm includes generating a plurality of laser beam pulses, directing theplurality of laser beam pulses through a mask to generate a plurality ofpatterned laser beams, and irradiating a portion of a selected region ofa film with one of the plurality of patterned beams having an intensitythat is sufficient to melt the irradiated portion of the film, whereinthe irradiated portion of the film crystallizes upon cooling. The filmmoves along a first translation pathway and the mask moves along asecond translation pathway while successive portions of the selectedregion are irradiated with patterned beams, such that the selectedregion of the film are substantially completely crystallized in a singletraversal of patterned beams over the selected region of the film.

In one or more embodiments of the present invention, the processprovides constant or oscillating motion of the mask in one direction,e.g., along the x-axis, while the film is continuously advanced inanother direction, e.g., along the y-axis. The resultant polycrystallinefilm possesses columns of elongated grains having long grain boundarieswhose locations are controlled by the spatially confined melting andcrystallization of the film.

In another aspect of the invention, a method for processing a filmincludes generating a plurality of laser beam pulses, directing theplurality of laser beam pulses through a mask having a mask pattern witha length l, a width w, and a spacing between adjacent patterns d togenerate a plurality of patterned laser beams, wherein each of thepatterned beams has a length l′, a width w′ and a spacing betweenadjacent patterned beams d′, and irradiating a portion of a region ofthe film with one of the plurality of patterned beams. The mask andpatterned beam proportions, e.g., w and w′, l and l′, and d and d′, arerelated by the demagnification factor of the projection optics. Thepatterned beam has an intensity that is sufficient to melt an irradiatedportion, and the irradiated portion crystallizes upon cooling. The filmis moved at constant velocity in a y-direction, and the mask is moved inthe x-direction while the film is irradiated with the patterned beam.The patterned beam is advanced a distance of about l′/n-δ in they-direction from the one irradiation pulse to the next, where δ is avalue selected to form an overlap in adjacent irradiated portions and adistance of about λ′, where λ′=w′+d,′ in the x-direction over a selectednumber of irradiation pulses n.

In one or more embodiments of the present invention, n is in the rangeof 2 to about 25. In one or more embodiments of the present invention, nis 2, the y-translation distance of the patterned beam is about l′/2-δ,and the x-translation of the patterned beam distance is about λ′/2.

In one or more embodiments of the present invention, the processprovides constant or oscillating motion of the patterned beam in onedirection, e.g., along the x-axis, while the patterned beam is alsocontinuously advanced in another direction, e.g., along the y-axis. Theresultant polycrystalline film possesses columns of elongated grainshaving long grain boundaries (substantially aligned with the length ofthe column) whose locations are controlled by the spatially confinedmelting and crystallization of the film.

According to one embodiment of the present invention, the x- andy-translations of the patterned beam are selected to provide columns ofelongated polycrystalline material that are positioned at an anglerelative to the axes of translation.

In another aspect of the invention, a device includes a polycrystallinethin film having columns of elongated crystal grains separated bylocation-controlled grain boundaries that are tilted at an angle theta(θ) with respect to an edge of the thin film substrate, wherein θ isgreater than 0° and ranges up to about 45°. Theta (θ) is referred to asthe “tilt angle” of the column of crystallized material.

In another aspect of the invention, a device containing apolycrystalline thin film transistor (TFT) includes a polycrystallinethin film defined by x- and y-axes. A TFT device is located in the thinfilm and is substantially aligned with the x- and y-axes of the thinfilm. The polycrystalline thin film has a periodic polycrystallinestructure including columns of elongated crystal grains. A column issubstantially aligned with the x- and y-axes of the film; however, theelongated crystals within the column contain location controlled grainboundaries that are oriented at an angle with respect to the x- andy-axes of the film. The TFT device is positioned at an angle withrespect to the grain boundaries of the elongated crystals. In one ormore embodiments, the number of long grain boundaries in each thin filmtransistor device remains substantially uniform.

In one aspect, the method avoids the need to scan the same area of thesubstrate multiple times in order to fully crystallize the film. It alsoprovides a simpler and time-efficient process that translates the systemin the x- and y-directions during laser irradiation. Furthermore, itprovides grains that are elongated beyond their characteristic lateralgrowth length, thereby further improving the crystalline properties ofthe polycrystalline film.

BRIEF DESCRIPTION OF THE DRAWING

Various features of the present invention can be more fully appreciatedwith reference to the following detailed description of the inventionwhen considered in connection with the following drawing, in which likereference numerals identify like elements. The following figures are forthe purpose of illustration only and are not intended to be limiting ofthe invention, the scope of which is set forth in the claims thatfollow.

FIG. 1 is a schematic illustration of an exemplary system for performinga sequential lateral solidification process according to one or moreembodiments of the present invention.

FIG. 2 is a schematic illustration of a mask for use in a sequentiallateral solidification process according to one or more embodiments ofthe present invention.

FIG. 3 shows an exemplary irradiation path of laser beam pulses on asample surface as the sample is processed using the system of FIG. 1.

FIGS. 4A-4F show the laser beam irradiation patterns and portions of theresulting grain structures obtained during sequential laser beamprocessing on an exemplary first column of a sample having a filmthereon.

FIG. 5 illustrates the first step in the sequential lateralsolidification of an exemplary second column of a sample having a filmthereon.

FIG. 6A illustrates the mask position during translation in the constanty-direction and oscillating x-direction as a linear step function, FIG.6B shows the mask position during translation in the x- and y-directionsas a sinusoidal function, FIG. 6C shows the mask position duringtranslation in constant x- and y-directions as a linear step function;and FIG. 6D shows the mask position during translation in constant x-and y-directions as a linear continuous function.

FIG. 7 illustrates a series of laser beam irradiation positions in afour-cycle (n=4) sequential lateral solidification process according toone or more embodiment of the present invention.

FIG. 8 shows another exemplary irradiation path of laser beam pulses ona sample surface as the sample is processed using the system of FIG. 1.

FIG. 9 is a schematic illustration of an irradiation pattern andresultant polycrystal grain formation according to one or moreembodiments of the present invention during sequential laser beamprocessing on an exemplary first column of a sample having a filmthereon.

FIG. 10 is a schematic illustration of a film processed according to oneor more embodiments of the present invention in which the substrate ispositioned along x′- and y′-axes and is offset from the x- and y-axes oftranslation during sequential laser beam irradiation. The irradiationsequence includes oscillation of the mask in the ± x-directions.

FIG. 11 is a schematic illustration of a film processed according to oneor more embodiments of the present invention in which the substrate ispositioned along x′- and y′-axes and is offset from the x- and y-axes oftranslation during sequential laser beam irradiation. The irradiationsequence includes translation of the mask in a constant x-direction.

FIG. 12 is a schematic illustration of a TFT device having integrationregions and pixel regions positioned at an angle with respect to thelong, location-controlled grain boundaries of the polycrystalline film.

FIG. 13A is a schematic illustration of a mask to be used in one or moreembodiments of the present invention; FIG. 13B is a diagram illustratinga mask translation pattern for the mask of FIG. 13A, and FIGS. 13C and13D illustrate the x-position and y-position, respectively, of the maskduring the translation pattern of FIG. 13B.

FIG. 14 is a schematic illustration of an irradiation pattern accordingto one or more embodiments of the present invention during sequentiallaser beam processing using a mask pattern shown in FIG. 13A and a masktranslation pattern shown in FIG. 13B.

FIG. 15 is a schematic illustration of the sequential irradiation of afilm according to one or more embodiments of the present invention usinga mask pattern shown in FIG. 13A and a mask translation pattern shown inFIG. 13B.

FIG. 16 is an illustration of a crystallized film processed according toone or more embodiments of the present invention using the masktranslation of FIGS. 14 and 15.

DETAILED DESCRIPTION OF THE INVENTION

Sequential lateral solidification is a particularly useful lateralcrystallization technique because it is capable of grain boundarylocation-controlled crystallization and provides crystal grains ofexceptionally large size. Sequential lateral solidification produceslarge grained structures through small-scale translation of a thin filmbetween sequential pulses emitted by a pulsed laser. As the film absorbsthe energy of each pulse, a small area of the film melts completely andrecrystallizes laterally from the solidus/melt interface to form acrystalline region. By “lateral crystal growth” or “lateralcrystallization,” as those terms are used herein, it is meant a growthtechnique in which a region of a film is melted to the film/surfaceinterface and in which recrystallization occurs in a crystallizationfront moving laterally across the substrate surface. “Characteristiclateral growth length,” as that term is used herein, means the length ofunimpeded lateral growth of a crystalline grain in a single irradiationstep under set irradiation conditions and sample configuration.

The thin film may be a metal or semiconductor film. Exemplary metalsinclude aluminum, copper, nickel, titanium, gold, and molybdenum.Exemplary semiconductor films include conventional semiconductormaterials, such as silicon, germanium, and silicon-germanium. Additionallayers situated beneath or above the metal or semiconductor film arecontemplated. The additional layers can be made of silicon oxide,silicon nitride and/or mixtures of oxide, nitride or other materialsthat are suitable, for example, for use as a thermal insulator toprotect the substrate from overheating or as a diffusion barrier toprevent diffusion of impurities from the substrate to the film.

Referring to FIG. 1, an apparatus 100 is shown that may be used forsequential lateral solidification. Apparatus 100 has a laser source 120.Laser source 120 may include a laser (not shown) along with optics,including mirrors and lenses, which shape a laser beam pulse 140 (shownby dotted lines) and direct it toward a substrate 160, which issupported by a stage 170. The laser beam 140 passes through a mask 180supported by a mask holder 190. The mask holder is capable oftranslation in at least one direction. Exemplary laser beam pulses 140generated by the beam source 120 can provide a beam intensity in therange of 10 mJ/cm² to 1 J/cm², a pulse duration in the range of 10 to300 ns and a pulse repetition rate in the range of 10 Hz to 300 Hz.Currently available commercial lasers such as Lambda Steel 1000available from Lambda Physik, Ft. Lauderdale, Fla., can achieve thisoutput. Higher laser energy and larger mask sizes are possible withincreasing laser power. After passing through the mask 180, the laserbeam pulse 140 passes through projection optics 195 (shownschematically). The projection optics 195 reduces the size of the laserbeam and simultaneously increases the intensity of the optical energystriking the substrate 160 at a desired location 165. Thedemagnification in each direction is typically on the order of between3× and 7× reduction, for example, a 5× reduction, in image size. For a5× reduction, the image of the mask 180 striking the surface at thelocation 165 has 25 times less total area than the mask, correspondinglyincreasing the energy density of the laser beam pulse 140 at thelocation 165 by a factor of 25. Due to the demagnification effect of thelaser optics, the mask translation distance is greater than thetranslation distance of the beam where it impinges on the substrate. Thetranslation distances of the mask and of the beam on the substratesurface differ by approximately the demagnification factor of theprojection optics.

The stage 170 is a precision x-y stage that can accurately position thesubstrate 160 under the beam 140. The stage 170 can also be capable ofmotion along the z-axis, enabling it to move up and down to assist infocusing or defocusing the image of the mask 180 produced by the laserbeam 140 at the location 165. In another embodiment of the method of thepresent invention, it is possible for the stage 170 to also be able torotate.

A thin film is processed into a polycrystalline thin film by generatinga plurality of excimer laser pulses of a predetermined fluence,controllably modulating the fluence of the excimer laser pulses,homogenizing the intensity profile of the laser pulse plane, maskingeach homogenized laser pulse to define patterned laser beams,irradiating the thin film with the laser beams to effect melting ofportions thereof, and controllably and continuously translating thesample and the mask to move the patterned beam across the substratesurface. The laser pulse frequency and the movement (speed anddirection) of the sample are adjusted so that the areas of sequentialirradiation of the sample overlap from one irradiation/crystallizationcycle to the next, so as to provide for the lateral crystal growth thatgives rise to large grains. Pulse frequency and stage and mask positionmay be coordinated and controlled by a computer. Systems and methods forproviding continuous motion sequential lateral solidification areprovided in U.S. Pat. No. 6,368,945, which is incorporated in itsentirety by reference.

FIG. 2 shows a mask 200 having a plurality of slits 220 with slitspacing d 240. FIG. 2 alternatively illustrates an intensity patterngenerated on a substrate surface by an irradiation laser beam pulsedefined by the mask. As noted above, the mask dimensions and theintensity patterns are related by a scaling factor that is a function ofthe demagnification. The length l of the mask feature is indicated byarrow 250. In one or more embodiments, it is chosen to be commensuratewith the dimensions of the device that is to be fabricated on thesubstrate surface. The width w of the mask feature is indicated by arrow260 and also can vary. The dimensions l and w are not shown to scale; inmany instances the length is considerably greater than the width. Inexemplary embodiments, width w is chosen to be small enough to avoidsmall grain nucleation within the melt zone, yet large enough tomaximize lateral crystalline growth for each excimer pulse. In one ormore embodiments, the slit spacing d 240 is less than the slit width260. The mask can be fabricated from a quartz substrate and includes ametallic or dielectric coating that is etched by conventional techniquesto form a mask having features of any shape or dimension.

The dimensions of the mask features may depend on a number of factors,such as the energy density of the incident laser pulse, the duration ofthe incident laser beam pulse, the thickness of the semiconductor thinfilm, the temperature and thermal conductivity of the substrate. Fromthe standpoint of processing efficiency, the width of the slit-shapedmask feature is as large as possible so as to maximize surface coverage.However, width is also determined by the desire to completely melt thethin film throughout its thickness and to avoid nucleation within themelted portions during crystallization. By way of example only, the maskfeature are of a dimension sufficient to create a beam dimension in therange of about 0.5-1 mm long, about two to five micrometers (μm) wide,and a slit spacing of about one to three micrometers (μm). The actualmask dimensions are a function of the demagnification factor (discussedabove).

FIG. 3 shows an exemplary irradiation path 310 of beam pulses impingingon a thin film 300 as it is processed according to one or moreembodiments of the invention. The irradiation path 310 indicates thepath of the laser beam pulses as the substrate and the mask aretranslated in the x- and y-directions relative to a stationary laserbeam (although in one or more embodiments, it is contemplated that thelaser is capable of movement to provide some or all of the desiredtranslations). Arrows indicate the direction (and sequence) oftranslations. The translations are accomplished by the coordinatedmovement of the film-bearing substrate (on a movable stage) and themask. Dashed lines 390, 390 a, etc. define imaginary columns 395, 395 a,etc. on the substrate surface, each of which is irradiated andcrystallized in a single traversal of the laser across the substratesurface (or a selected region of the substrate surface). The magnitudeof the x- and y-translations are not shown to scale; and thex-translations are typically much smaller than the y-translations. Inone or more embodiments of the present invention, the sample movescontinuously in a straight line direction, e.g., in the positivey-direction or in the negative y-direction, and the mask is translatedin the transverse direction, e.g., ± x-direction. The mask may oscillateback and forth in the x-direction, e.g., ±−x-direction, or it may movecontinuously in a straight path, e.g., in the positive x-direction. Inone or more embodiments of the present invention, the mask translates inboth the x- and y-directions.

Processing according to one or more embodiments of the present inventionis described with reference to FIG. 2 and FIG. 3. The mask and the stageon which the sample is located are positioned to provide an illuminationpattern at an initial position 315 (shown by dotted lines in FIG. 3)where the pulsed laser beam passing through the mask generates a firstintensity pattern on the film. For reasons that will become apparent inthe discussion that follows, only a portion, e.g., one-half, of the maskis used for the first irradiation step. That is, the sample ispositioned under the mask so that, for example, ½ l of the slit length250 of mask 200 is exposed onto the substrate surface. The sample movescontinuously in the y-direction at a velocity that is calculated toposition the sample in the correct location relative to the mask by thetime the laser pulses again. Thus, the sample moves in the positivey-direction a distance 320 that results in the repositioning of theillumination pattern. The distance is a function of the mask dimensionsand the inverse of the laser demagnification factor and is less thanhalf the length of the projected illumination pattern, i.e., the“projected length,” of the mask slit, i.e., l′/2-δ, where l′ is theprojected length of the mask slit and δ is a small value to ensure thatthe irradiated portions of the film overlap from a first irradiationposition to the next. In an exemplary embodiment, δ is about 1-10% ofthe projected length l′. During this time, the mask also ismicrotranslated a distance 325 in the positive x-direction that is about½λ, where λ is the distance from the leading edge of the first mask slitto the leading edge of the next adjacent slit, shown as arrow 270 inFIG. 2, i.e., λ=w+d. Note, however, that the beam dimension moves only adistance of ½λ′ due to the demagnification factor of the laser beam. x-and y-translations are designed so that the sample and mask are inposition for the next laser pulse. It will be appreciated that, whilethe translation distances of both the mask and the substrate are afunction of the mask dimensions, they are typically located at oppositesides of the laser demagnification process, and the actual translationdistances are adjusted accordingly.

After the first translation, the illumination pattern is at position 315a (shown in FIG. 3 by small dashed lines). In one or more embodiments ofthe present invention, the irradiated pattern at position 315 a overlapsslightly with adjacent column 395 a, which ensures that the full samplesurface is irradiated. The overlap is selected to maximize extent of thefilm coverage, while ensuring that the film surface is fully irradiated.The width of the overlap is small, and can be, for example, 0.5 μm, 1μm, 1.5 μm, or greater. A second laser beam pulse generates a secondintensity pattern on the film. Next, the sample is further translated inthe positive y-direction along path 320 a and the mask is translated inthe negative x-direction along path 325 a to arrive at position 315 b(shown as large dashed lines in FIG. 3). Sample translation continues inthis manner along path 320 b, 325 b, etc. until the sample reaches apredetermined endpoint.

Upon reaching the predetermined endpoint, a single scan or translationof the sample region is complete, and the sample is moved along arrows380 to a new start position at a new column 395 a on the film andirradiation and translation in the reverse direction, e.g., alongirradiation path 340, 345, etc. is carried out. It will be appreciatedthat the sample is now translated continuously in the negativey-direction. In this manner, the entire surface of the thin film isirradiated without disruption of the pulsed laser. Although FIG. 3 showsan irradiation path that traverses from one edge of the substrate to theother edge of the substrate, it is within the scope of the invention todefine an irradiation path that traverses only a portion of a substrate.The endpoint can be at the sample edge or it can be a predeterminedlocation within the film, for example, when it is desired to crystallizeonly a portion of the film surface according to the process describedherein.

FIGS. 4A-4F illustrate the growing crystallization front with sequentialirradiation according to the laser beam irradiation path shown in FIG.3. The y- and x-axes orientations are as shown. FIG. 4A shows theirradiation and complete melting of areas 410 of the thin film 400 whenthe illumination pattern is at a first initial position 315. In one ormore embodiments of the present invention, optionally only one-half ofthe mask is exposed onto the film surface (i.e., position 315) in thefirst laser beam pulse in order to avoid non-irradiated regions at thefilm edge. The regions 435 of the film correspond to the beam-blockedslit spacings 240 of the mask and therefore remain solid. In anexemplary embodiment, regions 410 have a width of about 3 μm and a slitspacing of about 1.5 μm. After the irradiation laser pulse, the firstregions 410 rapidly cool and crystallize. Crystallization is initiatedat solid boundaries of region 418 and proceeds inward to the center ofregion 410. As shown in FIG. 4B, region 410 crystallizes to form twocrystallization growth fronts 420, 425 of elongated grains grownlaterally towards one another from adjoining unmelted regions 435. Thecharacteristic lateral growth length is a function of the filmthickness, the substrate temperature, pulse duration, buffer layering,mask dimensions, etc. The two crystallization growth fronts 420, 425abut one another along an abutment boundary 430 after the grains havegrown laterally, e.g., about 1.5 μm in the current example.

The substrate is advanced a distance in the positive y-direction and themask is translated a distance in the positive x-direction alongirradiation paths 320 and 325, respectively, to arrive at a secondposition 315 a with respect to the stationary laser beams. The timing ofthe laser pulse is controlled such that the translation of the mask andthe substrate are complete at the time of the next laser beam pulse.

As shown in FIG. 4C, a second irradiation laser beam pulse irradiatesand completely melts the substrate in second regions 450. Second regions450 are offset from the first regions 410 (shown as dashed lines FIG.4C) in the x-direction a distance so that the newly melted regions 450are nested between and overlap slightly the first regions 410. Thesecond regions 450 are also offset from the first regions 410 in they-direction so that the newly melted regions 450 extend an additionaldistance in the y-direction beyond regions 410. The pulse frequency andtranslation speed (of the mask and sample) are controlled, e.g., by acomputer, to provide the desired location and overlap of sequentialirradiations. As shown in FIG. 4C, the crystallized regions 410 can actas seed crystals for crystallization of melted regions 450. The width ofthe overlap is small, and can be, for example, 0.5 μm, 1 μm, 1.5 μm, orgreater. Overlap is sufficient to avoid unirradiated areas on thesemiconductor film and to provide seed crystal for subsequentcrystallization.

FIG. 4D shows the resultant microstructure of the film after cooling,resolidification and crystal growth of the completely melted regions 450shown in FIG. 4C. The melted region 450 crystallizes to form twocrystalline growth fronts 465, 468 that proceed towards each other fromthe adjoining non-irradiated regions 460 and crystallized regions 410.The two crystalline growth fronts abut one another along a grainboundary 469 after the grains have grown laterally. Furthermore, thegrains grown from the region of the melt that is in contact withpolycrystalline region 410 form elongated grains that are a continuationof the grains formed in region 410, resulting in crystallized regions470 having significantly increased grain lengths, e.g., greater than thecharacteristic lateral growth length.

During and after crystallization of regions 450 (the time scale ofsolidification is about 1-10 μsec, while the interval between two laserpulses is a few msec), the substrate advances a distance in they-direction and the mask is translated a distance in the negativex-direction along irradiation paths 320 a and 325 a, respectively, toarrive at a third position 315 b with respect to the stationary laserbeams, as shown in FIG. 4E. Because the y-axis translation distance overthe previous two translations is less than l′, the projected length ofthe mask slit, the third irradiation position 315 b overlaps previouslycrystallized regions 410. The timing of the third laser beam pulse iscontrolled in a manner similar to the control of the previous first andsecond laser beam pulses, so as to coincide with the proper positioningof the sample and the mask at position 315 b at the time of pulsing. Thethird laser beam pulse is generated to irradiate the sample substrate toform completely melted regions 480. As previously described, thetranslation provides overlapped areas to avoid non-irradiated regionsand to provide grains as seed crystals for crystallization. The meltedregions 480 resolidify and crystallize as described above.

The substrate continues to advance along the irradiation path shown inFIG. 3, and the process of irradiation, melt and crystallizationprogresses along column 395. FIG. 4F shows resolidification regions 485,which form column 395 of the processed film containing contiguousparallel elongated grains having grain boundaries generally oriented inthe x-direction. Column 395 is defined approximately by the distance ofy-translation and the overall width of the mask. Note that this regionhas been fully crystallized in a single pass over the substrate surface.

Upon complete crystallization of column 395, the sample is translatedalong path 380 to a new position corresponding to column 395 a of thesample. See FIG. 3. The process as described above can be repeated forcolumn 395 a, as is illustrated in FIG. 3, except that the sample nowmoves continuously across the film region to be crystallized in thereverse direction, e.g., in the −y direction, along irradiation path340, 345, etc.

FIG. 5 illustrates the first step in the sequential irradiation processfor column 395 a. The mask and substrate are in position to irradiateand melt a portion 410′ of the film, while a portion 435′ is notirradiated and remains solid. As discussed above, elongated grains (notshown) grow inwards towards one another from adjoining unmelted regions435′. Also as described above, the substrate and mask translate along aspecified pathway during pulsed laser irradiation of the film so as tocrystallize a column of the film in a single scan across the filmsurface. The translation path overlaps somewhat with the previouslycrystallized column 395. The overlap region 510 between adjacentirradiation regions of the first and second columns extends crystalgrowth from the previously laterally grown crystals. In this manner, theentire surface of the semiconductor film is processed to provide apolycrystalline film having highly elongated grains terminating in agrain boundary that is substantially aligned with the y-axis.

In one or more embodiments, the above process is characterized by maskoscillation between two x-axis positions, e.g., +x and −x, while thesample is continuously advanced in the same direction along the y-axis,e.g., +y. The exact mode of translation is not of great importance tothe invention, so long as the distances in the x- and y-directions arecarried out in coordination with the laser pulse frequency. Curves 610,615 illustrate the x-position of the mask with time during stepwise(FIG. 6A) or continuous (FIG. 6B) translation, respectively. Thus, byway of example, the x-translation can be a step function as shown inFIG. 6A, or it can be continuous, e.g., a sinusoidal function, asillustrated in FIG. 6B. Other modes of translation are within the scopeof the invention. Marks 620 on the x-translation curve indicate the maskposition at the moment of laser irradiation, that is, the mask issubstantially fully translated and in position at the time of laserirradiation.

In one or more embodiments of the present invention, the mask istranslated stepwise or continuously in a constant x-direction, while thesample is continuously moved in a y-direction. Curves 630, 635 showx-position of the mask with time during a stepwise (FIG. 6C) andcontinuous (FIG. 6D) process, respectively. Marks 640 indicate thex-position of the mask at the time of irradiation.

Although the x-axis oscillation introduces an additional process controlstep, it avoids the need to scan the same area of the substrate multipletimes in order to fully crystallize the semiconductor film. Furthermore,it provides grains that are elongated beyond their characteristiclateral growth length, thereby further improving the crystallineproperties of the polycrystalline film.

The foregoing examples describe an irradiation cycle consisting of twolaser pulses and two x,y-translations, i.e., a cycle consisting of npulses and n x,y-translations, where n=2. It is within the scope of thepresent invention to process a thin film using any number of sample andmask translation sequences to traverse an x-distance of about λ and ay-distance of about l′ (recall that l′ is related to l, the length ofthe mask feature, by a demagnification factor of the laser optics). Thevalue for n can vary widely, and can range, for example, from n=2-100.Without being bound by any mode or outcome of operation, higher n-valuestend to provide films of higher crystallinity, longer grains and fewergrain boundaries.

In one or more embodiments, a process is provided to fully irradiate asubregion defined by a mask feature of dimensions w, d, and l using “n”laser irradiation pulses and “n” sets of x,y-translations, e.g.,hereafter referred to as an “n-irradiation cycle.” According to anexemplary embodiment, the sample moves a distance of about l′/n-δ in they-direction between laser pulses. Translation distance of the mask inthe x-axis between laser pulses is selected such that a total distanceof λ is traversed over the sum of “n” cycles. Each x-translation can bethe same or different, stepped or continuous. In one or moreembodiments, each x-direction translation is substantially the same andcan be λ/n. The selection criteria for the length and width of the maskfeatures are similar to those described above for a mask used in thetwo-cycle irradiation process of FIGS. 4A-4F. However, the slit spacingbetween adjacent mask spacings can vary. In one or more embodiments, theslit spacing is greater than the slit width w. In one or moreembodiments, the slit spacing and x-translation distance is selected toensure x-direction overlap in sequential irradiation patterns.

This process is illustrated schematically in FIG. 7, for the case wheren=4. FIG. 7 depicts an enlarged portion of a film 700, which isirradiated by an irradiation pattern including at least two projectedpatterns 701, 701 a spaced apart from each other by an exemplary spacing740. The spacing 740 is not shown to scale; the spacing can be larger orsmaller than shown. The sample is processed using a translation sequencethat moves the sample a distance of l′-δ and the mask as distance ofabout λ during the time it takes for the laser to pulse four times. Byway of example, the first irradiation pattern is at position 701, 701 a(shown in FIG. 7 with solid lines), and the mask is offset to exposeonly a portion of the sample. The sample moves a distance of aboutl′/4-δ in the y-direction (indicated by arrow 712), and the mask istranslated a distance of about λ/4 in the x-direction (indicated byarrow 710) to position 702, 702 a (shown in FIG. 7 with dotted lines),where the sample again is irradiated and recrystallized. x,y-translation(λ/4, l′/4-δ), irradiation and crystallization continue throughpositions 703, 703 a (shown in FIG. 7 with dashed lines) and 704, 704 a(shown in FIG. 7 with dotted/dashed lines). Each irradiation andcrystallization increases the grain length of the polycrystalline grainsby using the previously crystallized grains as seed crystals for lateralgrain growth. If the x-translation is selected to be less than thelateral growth length of the semiconductor grains, then extremely longgrains can be obtained. Once the mask has translated a distance of aboutλ in the x-direction and the sample has translated a distance of l′-δ inthe y-direction, the sample and the mask are repositioned to irradiatethe next region of the sample. For example, the mask is translated adistance of about −λ in the x-direction; and the sample is translated adistance of about l′/4 in the y-direction to reposition the sample atlocation 720 (shown in FIG. 7 with bold lines), where thecrystallization process is repeated. In the above exemplary process,distances of about λ and about l′ are traversed in an n=4 irradiationcycle. It will be immediately apparent to those of skill in the art thatany value of ‘n’ can be employed and that the translation distances areadjusted accordingly.

A crystallized column can also be generated using stepwise or continuousmovement of the mask in a constant x-direction. By way of example, FIG.8 illustrates an irradiation path 805 that can be obtained using aconstant x-direction translation of the mask. Each set ofx,y-translations shifts the irradiation path in the direction indicatedby lines 825, 825 a, 825 b, etc., so that the resulting crystallizedregions advance in a constant x (and y) direction across a film surface800. In contrast to an oscillating mask translation, which providescolumns of elongated crystals oriented along (parallel to) the longdimension (y-axis) of the substrate, a constant x-direction translationresults in tilted or diagonal columns 895, 895 a (defined by imaginarylines 890, 890 a) that “walk across” the substrate surface at an angle.Crystallization proceeds in a manner similar to that shown in FIGS.4A-4F for an oscillating mask translation process, with the exceptionthat the irradiation pattern is incrementally offset in a constantx-direction.

In an exemplary process, the sample and the mask are positioned toprovide an illumination pattern at an initial position 815 (shown bydotted lines in FIG. 8), where the pulsed laser beam passing through amask generates a first intensity pattern on the film. As discussed abovefor oscillating mask translation, only a portion of the mask is used forthe first irradiation step. The sample then moves a distance 820 in thepositive y-direction, e.g., l′/2-δ, where l′ is a function of the lengthof the mask feature and the demagnification factor of the laser opticsand δ is a small value to ensure that the intensity patterns overlapfrom one irradiation position to the next; and the mask translates adistance 825 in the positive x-direction, e.g., about ½λ, where λ=w+d.As in the case of an oscillating mask translation, x- and y-translationcan occur sequentially, in any order, or simultaneously.

The mask and sample move to position 815 a (shown in FIG. 8 by smalldashed lines) in time for a second laser beam pulse, which generates asecond intensity pattern on the film. The substrate continues to move inthe positive y-direction along path 820 a and the mask continues totranslate in the positive x-direction along path 825 a to arrive atposition 815 b (shown as large dashed lines in FIG. 8). x,y-translationcontinues in this manner along path 820 b, 825 b, and 820 c, 825 c, etc.until the substrate reaches a predetermined endpoint. Thus, theirradiation path for column 895 is characterized by continuous motion ofthe substrate in the positive y-direction and continuous translation ofthe mask in the positive x-direction. When the scan of the first columnis complete, the substrate is repositioned by moving the substrateand/or mask along the path defined by arrows 880. Translation of thesubstrate and mask in the return direction, e.g., along irradiation path840, 845, etc., concurrent with irradiation of the film, occurs tocrystallize column 895 a. Because the resultant crystallized columns arenot parallel to the sample edge, a lower left-hand region 870 (and acorresponding upper right hand region) is not crystallized during theprocess. If it is desired to crystallize region 870, the region iscrystallized in a separate irradiation step using an irradiation pathwaysimilar to that already described.

In other exemplary embodiments, the irradiation/crystallization sequenceis carried out over “n” cycles, as described above for the oscillatingmask process. ‘n’ can range, for example, from about 2 to 100, or more.

With reference to FIG. 9, crystallization of a film 900 is shown usingmask translation in the constant x-direction. Irradiation of a laserbeam through a mask having five (5) slits produces an irradiationpattern 910 (indicated by bold lines in FIG. 9). Note that the x and ydirection are not drawn to scale and that the length can be greater thanactually shown. Further, slits typically may be wider than shown. Theirradiation pattern steps across the sample to form a crystallizedcolumn 920, 920 a, etc., which extends the length of the irradiatedsection (shown bounded by imaginary boundary 925, 925 a, etc.). Anenlarged portion of column 920 is shown in inset 925, which serves toillustrate the grain growth and orientation. Column 920 containscontiguous, elongated crystal grains 940 bounded by longlocation-controlled grain boundaries 950 that are generally parallel tothe y-direction of translation. Individual elongated grains 940 alsohave substantially parallel grain boundaries 960 that are generallyoriented in the x-direction. Due to the constant step in thex-direction, columns 920 are tilted with respect to the sample edge (andthe y-translation axis) at a tilt angle θ 965. The magnitude of θ is afunction of the x,y-translation of the substrate and mask.

The crystallization pattern such as shown in FIG. 9 results when theedges of the substrate are aligned with the x- and y-translation axes.Alternatively, the substrate can be positioned on the movable table sothat it is at an angle with respect to the x- and y-translation axes,that is, the edges of the substrate (or imaginary edges in the case of around or irregularly shaped substrate or subregion of the film) aretilted at an angle φ with respect to the x- and y-translation axes. Theorientation difference between the x- and y-translational axes and thesubstrate, e.g., the misalignment angle, provides an additional degreeof control over the location and orientation of polycrystals grown inthe crystallization process according to one or more embodiments of thepresent invention.

FIGS. 10 and 11 illustrate various methods and crystallization patternsthat may be obtained using a single scan irradiation process onsubstrates that are misaligned with the translation axes.

FIG. 10 is a schematic illustration of a crystallized film 1000 that hasbeen processed using an oscillating mask translation process, that is,where the mask oscillates in the positive and negative x-directions. Thesubstrate (with film) is placed on stage 1010 along x′- and y′-axes thatare at an angle φ (indicated by arrow 1023) with respect to the x- andy-translation axes. As used herein, x,y-misalignment is a measure of thedifference between the x-y-translational axes and the real (orimaginary) x′,y′-axes defining the substrate edges. The film isprocessed in an oscillating mask translation process such as isdescribed above (see, e.g., FIGS. 3-5), resulting in a crystallized filmcontaining columns 1020 that are parallel to the y-axis of translation,but offset from the substrate y′-axis of the film substrate at an anglecommensurate with angle φ, the angle of x,y-misalignment. Inset 1040illustrates the crystalline grain structure of the film in greaterdetail. Although columns 1020 form diagonally across substrate 1000, thelocation-controlled grain boundaries 1055 of elongated crystal grains1030 form parallel to the y-translation axis.

An alternative crystalline grain structure is obtained when the mask istranslated in a constant x-direction. FIG. 11 is a schematicillustration of a crystallized film 1100 that has been processed usingconstant x-translation of the mask on a substrate that is aligned alongaxes x′ and y′ and offset from the x- and y-translational axes by anangle, φ. The substrate (with film) is placed on a stage 1110 along x′-and y′-axes that are at an angle φ with respect to the x- andy-translation axes. In one or more embodiments where the angle φ ofx,y-misalignment (indicated by arrow 1125) is of the same magnitude asthe tilt angle θ (see, FIG. 9 and related discussion above), theresultant columns 1120 are parallel to the x′- and y′-axes of thesubstrate. Thus, by way of example only, if the column tilt angle θ is10°, and the substrate is rotated at a misalignment angle φ of 10°, thenthe resultant polycrystalline columns 1120 are substantially parallel tothe y′-axis. Although columns 1120 run parallel to the substratey′-axis, the elongated grains contained within the columns nonethelessremain oriented relative to the x,y-translation axes. Thus, theelongated crystal grains 1130 (shown in inset 1140) containlocation-controlled grain boundaries 1155 that are substantiallyparallel to the y-translation axis. Although columns 1120 aresubstantially parallel to the substrate edge, the grains containedtherein are referred to as “tilted” because the long location-controlledgrain boundary 1155 is not parallel to the substrate edge.

Tilted grains find many applications in fabrication of micro-electronicdevices, for example, in the formation of thin film transistors (TFT)having active channel regions with uniform performance. The performanceof a TFT depends, in part, on the electron mobility of the semiconductorpolycrystalline layer, which depends, in part, on the number of grainboundaries in the TFT active channel. There will be certain deviceorientations where optimization of device uniformity (rather than deviceperformance) is desired. In a tilt-engineered device, each thin filmdevice is tilted (relative to the substrate edge) so that the samenumber of perpendicular grain boundaries is found in the active channelregion. Each device, therefore, has comparable mobilities andperformances. For example, co-pending International Application SerialNumber PCT/US02/27246, filed Aug. 27, 2002, and entitled “Method toIncrease Device-To-Device Uniformity for Polycrystalline Thin-FilmTransistors by Deliberately Misaligning the Microstructure Relative tothe Channel Region,” recommends that the TFT active channel is placed atan angle relative to the long location-controlled grain boundaries ofthe semiconductor film. However, forming TFT active channels (whichtypically involves conventional semiconductor fabrication steps such aspatterning and ion implantation) at such irregular angles is inefficientand not easily integratable into standard fabrication processes.

According to exemplary embodiments of the present invention, a TFTdevice contains active channels arranged at regular and orderedintervals, while maintaining a desired tilt angle of thelocation-controlled grain boundaries. FIG. 12 illustrates amicroelectronic device 1200 including a number of TFT devices 1210formed on a silicon polycrystalline film 1215. Each TFT device containsa pixel control area 1220, a row integration region 1230 and a columnintegration region 1240. The TFT device is typically formed in thesemiconductor film using a series of well-known, conventional ionimplantation and patterning methods. Stitch line 1225 denotes animaginary boundary between adjacent polycrystalline columns 1235, whereeach column is formed in a continuous scan of the sample by thepatterned laser beams. Note that the edge 1224 of the TFT device is inalignment with the film edge 1223 and stitch line 1225, but that edge1224 is tilted with respect to the location-controlled grain boundary1248. As shown in greater detail in inset 1232, column 1235 containspolycrystalline grains 1245 having a location controlled grain boundary1248 that is at a tilt angle θ with respect to the edges of the TFTdevice 1224. See, e.g., FIG. 11 and its discussion, above. Thus, aplurality of TFT devices 1210 are formed at regular and orderedintervals across the film substrate. The TFT devices are substantiallyaligned with the film edge 1223 and/or the stitch line 1225 of thepolycrystalline film; however, the TFT devices 1210, and in particular,the integration regions 1230 and 1240, are tilted at an angle withrespect to long location-controlled grain boundaries 1248 of thepolycrystals. This represents a significant improvement in deviceuniformity without increase in fabrication costs.

FIG. 13A illustrates another exemplary mask that is used in one or moreembodiments of the present invention. Mask 1300 is an inverted maskwhere regions or “dots” 1320 correspond to the laser-opaque, maskedregion and the remainder of the mask 1321 is laser-transparent. Uponirradiation, all but the regions masked by 1320 melt, and the solidislands serve as seeding sites for lateral crystal growth. The size andlocation of dots 1320 are selected so that the laterally grown regionsoverlap between successive irradiations.

In one or more embodiments of the present invention, a film iscrystallized using an inverted masked 1300 such as the one shown in FIG.13A, where opaque regions 1320 correspond to the masked region and theremainder of the mask 1310 is transparent. The mask 1300 is sequentiallytranslated in both the x- and y-directions about an imaginary centralpoint 1350 on the sample as shown in FIG. 13B. The mask sequence isdescribed as a series of motions of opaque region 1320′, however, it isunderstood that the entire mask, which may contain a plurality of opaqueregions, is moving in the sequence described.

With reference to FIG. 13B, the film is irradiated with a first laserpulse while the mask is at position A. Region 1320′ then is translated ashort distance 1330 in the x,y-directions from its original position Ato a new position B. After a second laser pulse at position B, the maskis translated a second distance 1335 in the x,y-direction to arrive atposition C. After a third laser pulse while at position C, the mask thentranslates a third distance 1340 to arrive at position D. A finalx,y-translation 1345 returns the mask region 1320′ to its originalposition A. The x- and y-coordinates of opaque region 1320′ at eachposition are shown in FIGS. 13C and 13D, respectively. During thesequential movement of the mask, the substrate moves in a constanty-direction.

FIG. 14 illustrates an irradiation sequence using mask 1300 according toone or more embodiments of the invention. The mask and the stage onwhich the sample is located are translated to provide an illuminationpattern 1400. The irradiation path 1400 indicates the path of the laserbeam pulses as the substrate and the mask are translated in the x- andy-directions relative to a stationary laser beam. Arrows indicate thedirection (and sequence) of translations. The translations areaccomplished by the coordinated movement of the film-bearing substrate(on a movable stage) and the mask. Dashed lines 1495, 1495 a, etc.define imaginary columns 1490, 1490 a, etc. on the substrate surface,each of which is irradiated and crystallized in a single traversal ofthe laser across the substrate surface (or a selected region of thesubstrate surface).

FIG. 15 illustrates the location of the opaque regions on the filmsample after the series of irradiation/translation steps shown in FIG.14. For the purpose of this example, the method is described withreference to a mask having a 1×12 array of opaque regions, however, itis understood that the mask can include any number and arrangement ofopaque regions. For clarity in FIG. 15, the location of the row ofopaque regions after each translation/irradiation cycle is denoted bynumbers, e.g., the location of the opaque regions during the firstirradiation is indicated by number “1”; the location of the opaqueregions during the second irradiation is indicated by number “2”, and soforth. It will also be appreciated that the translation distances ofboth the mask and the substrate are a function of the mask dimensionsand the laser demagnification.

The mask and sample are positioned for an initial irradiation. Thesample is moved continuously in the y-direction a distance 1410, whilethe mask also is microtranslated a distance 1415 in the x- andy-directions. The sample and mask are moved at a velocity that iscalculated to position the sample in the correct location relative tothe mask in time for the laser pulse. The illumination pattern isindicated in FIG. 15 by the row of 1's in column 1495. Duringirradiation, the sample is melted over the entire irradiated area exceptunder the opaque regions of the film. In the cooling that follows,crystal grains grow laterally from the solid front of the opaqueregions. After irradiation of the mask at the initial position, thesample moves continuously in the y-direction a distance 1420 at avelocity that is calculated to position the sample in the correctlocation relative to the mask by the time the laser pulses again. Duringthis time, the mask also is microtranslated a distance 1425 in the x-and y-directions, so that the mask is in position for the next laserpulse. The second irradiation is denoted in FIG. 15 by the row of 2's.In the current embodiment, by way of example only, the time betweenlaser pulses permits the sample to move the distance of three opaqueregion (indicated by arrow 1510 in FIG. 15), so that the secondirradiation pattern is offset by three opaque regions. The sample can,of course, move at any desired rate, and the irradiation pattern canhave any desired offset.

The continued translation of the sample along pathway 1430 and themicrotranslation of the mask in the x- and y-directions along pathway1435 positions the sample for the third irradiation, denoted in FIG. 15by a row of 3's. Note that a further (second) set of three opaqueregions (indicated by arrow 1520) is now beyond the irradiation area ofthe third laser pulse. The continued translation of the sample alongpathway 1440 and the microtranslation of the mask in the x- andy-directions along pathway 1445 positions the sample for the fourthirradiation, denoted in FIG. 15 by a row of 4's. Note that a further(third) set of three opaque regions (indicated by arrow 1530) are beyondthe irradiation area of the fourth laser pulse, but that a set of threeopaque regions were irradiated by all four laser pulses. If fullcrystallization of the film surface is desired, the mask can be offsetas described above for the mask pattern in FIGS. 3-5.

In one or more embodiments of the present invention, the irradiatedpattern at position overlaps slightly with adjacent column 1495 a, whichensures that the full sample surface is irradiated. The overlap isselected to maximize extent of the film coverage, yet to ensure that thefilm surface is fully irradiated. The width of the overlap is small, andcan be, for example, 0.5 μm, 1 μm, 1.5 μm, or greater.

After four laser pulses, a region of the film exemplified by circle 1560is completely irradiated. The opaque region designated as “1′” indicatesa fifth laser irradiation where the mask has returned to its originalposition A. Sample translation continues in this manner along path1420′, 1425′, 1430′, 1435′, 1440′, 1445′, etc. until the sample reachesa predetermined endpoint. In sum, the sample moves with constantvelocity in the y-direction, while the mask moves in both the x- andy-directions with the appropriate microtranslations to obtain thedesired crystalline film.

If the distance between adjacent opaque regions 1320 on mask 1300 isgreater than two times the characteristic lateral growth length of thefilm, then a crystallized structure surrounded by a small-grainedpolycrystalline precursor film is formed. Note that under somecircumstance “complete irradiation” may result in some regions havingsmall polycrystalline grains. As noted above, complete crystallizationdoes not require that the entire film have large grains. It merelyrequires that the region be crystallized to the extent desired by theprocess, such that the process does not require the laser to againtraverse the same subregion of the film. If the separation distance isless than or equal to the characteristic lateral growth length, thenadjacent crystallized structures will form abutting grains and theentire irradiated film forms contiguous large crystalline grains. Thisstructure is illustrated in FIG. 16.

Although various embodiments that incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatincorporate these teachings.

By way of example only, it is within the scope of the invention todefine an irradiation path that traverses only a portion of a substrate.It is also apparent that the choice of (x,y) as the coordinate system isarbitrary; the process can also be conducted using another set ofcoordinates. The sample can also be translated in the negative-y andpositive-x direction during irradiation, or the laser source may bemoved during operation to achieve one or more of the directionaltranslations.

1. A method of processing a selected region of a film on a substrate ina single scan, comprising: generating a plurality of laser beam pulses;directing the plurality of laser beam pulses through a mask to generatea plurality of patterned laser beams; irradiating a portion of aselected region of a film with one of the plurality of patterned beams,said beam having an intensity that is sufficient to melt the irradiatedportion of the film, wherein the irradiated portion of the filmcrystallizes upon cooling, moving the film along a first translationpathway and moving the mask along a second translation pathway whilesuccessive portions of the selected region are irradiated with patternedbeams, such that the selected region of the film is substantiallycompletely crystallized in a single traversal of the patterned beamsover the selected region of the film; wherein the film moves in aconstant direction along the first translation pathway during a singletraversal of the patterned beams over the selected region of the film.2. The method of claim 1, wherein the film and the mask move inorthogonal directions.
 3. The method of claim 1, wherein the film movesat a constant velocity along the first translation pathway.
 4. Themethod of claim 1, wherein the mask oscillates in positive and negativedirections along the second translation pathway during a singletraversal of the patterned beams over the selected region of the film.5. The method of claim 1, wherein the mask moves in a constant directionalong the second translation pathway during a single traversal of thepatterned beams over the selected region of the film.
 6. The method ofclaim 5, wherein the mask moves at a constant velocity along the secondtranslation pathway during a single traversal of the patterned beamsover the selected region of the film.
 7. The method of claim 1, whereinthe mask moves in more than one direction along the second translationpathway during a single traversal of the patterned beams over theselected region of the film.
 8. The method of claim 1, wherein thesubstrate is defined by x- and y-axes and the film moves in they-direction and the mask moves in the x-direction.
 9. The method ofclaim 1, wherein the substrate is defined by x- and y-axes and the filmmoves in the y-direction and the mask moves in the x- and y-directions.10. The method of claim 1, wherein laser pulse frequency and first andsecond translation pathways and speeds are selected so that irradiationoccurs at the desired location on the film.
 11. The method of claim 1,wherein the substrate is defined by x′- and y′-axes and the x′- andy′-axes of the substrate are offset from the translation directions offilm and mask by an angle θ, where θ is greater than 0° and ranges up toabout 45°.
 12. The method of claim 1, wherein the mask comprises aplurality of elongated laser-transparent regions in a laser opaquebackground.
 13. The method of claim 12, wherein the elongated regionscomprise rectangular regions.
 14. The method of claim 1, wherein themask comprises a plurality of laser-opaque features in alaser-transparent background.
 15. The method of claim 14, wherein themovement of the mask defines a pathway about a central location.